The purpose of this project is to determine which hormones and nutrients regulate protein turnover in skeletal muscle. The experimental model used in these studies is an isolated perfused preparation of rat hemicorpus which is mainly skeletal muscle and is free of endocrine glands. The aim is to localize the effects of hormones to specific steps in protein synthesis and degradation. The role of insulin in the regulation of the activity of the initiation factor, IFE2, is being investigated and related to the effects of the hormone on protein synthesis. The effects on protein turnover of corticosteroid, growth hormone, and thyroxone treatments, as well as the respective hormone deficient states, and the direct in vitro effects of the hormones, are being investigated. Changes in amino acid release resulting from alterations in protein turnover, or amino acid synthesis and catabolism, are also being evaluated. BIBLIOGRAPHIC REFERENCES: Baker, H.W.G., Worgul, T.J., Santen, R.J., Jefferson, L.S. and Bardin, C.W., Effect of prolactin on nuclear androgens in perfused male accessory sex organs. Proc. 3rd Annual Workshop on the Testis, Pittsburg, 1976. Rannels, D.E., Pegg, A.E., Rannels, S.R., Jefferson, L.S. and Morgan H.E., Decreased initiation factor activity in skeletal muscle of starved rats. Fed. Proc. 37: 1516, 1976.